i saw a tech page on the net that talked about overclocking the celeron d 2.66 cpu. they said they got to 3.8 with it with ease. the benchmarks for it at 3.8 looked real good too. not bad for a cheap cpu eh?
http://www.xbitlabs.com/articles/cpu/display/celeron-d_9.html
http://www.xbitlabs.com/articles/cpu/display/celeron-d_9.html